Before our introduction to traditional Chinese medicine, I have to make sure that everyone understand the concept of the Five Elements, namely Metal, Wood, Water, Fire and Earth. In ancient China, the theory of the Five elements was widely used as a tool to explain the worlds development and decline, and is still influencing our ways of thinking. Some people may say this is ridiculous or superstition. But since this theory has been popular for such a long time, it must make some sense. The Five Elements theory is very simple. As we can see in the diagram, metal engenders water, water engenders wood, wood engenders fire, fire engenders earth, and earth engenders metal. Then the restriction relationship. Metal restricts wood, wood restrict earth, earth restricts water, water restricts fire, and fire restricts metal. Now, you may be wondering what this theory has to do with traditional Chinese medicine. Well, thats what I am going to explain. First, lets talk about five internal organs of the body, the heart, liver, spleen, lungs, kidneys. And we believe that lungs belongs to metal, kidney belongs to water, liver belongs to wood, heart belongs to fire, spleen belongs to earth. Consequently, the five organs have the same relationship of engender and restriction. For example, if the heart fire become too strong, the lung metal will be weaken, then the liver wood become stronger, then the earth spleen decays, then the water kidney will be strengthened, which in turn restricts the fire of heart. To give you some proof of this theory, I will introduce something more about five elements theory. In fact, the five elements theory can not only be applied to explain the relationship between five organs, there are more. Such as five seasons, autumn belongs to metal, winter belongs to water, spring belongs to wood, summer belongs to fire, late summer belongs to earth. Similarly, we give the opinion without explanation. Now, lets see how it works. In spring, the wind comes from the east, and the trees start to grow. And the liver can easily catch disease in this season, in other word， the liver wood can be easily weaken. As a result, the heart fire grow stronger, people are usually in a good mood. To keep five organs in balance, we can try eating something sour to strengthen the liver wood. The other elements can be expressed in the same way. And these experiences have been proved by our daily lives for a thousand times. So we can see, everything in the world is connected. Only if we follow the rule of 5 elements theory, can we attain the harmony between human and nature and enjoy a healthy and happy life.